The present invention relates to a rotation transfer device for coupling a driven shaft and a driving shaft removably in the axial direction, and a paper feeding apparatus and an image forming apparatus including the rotation transfer device in which paper is fed along a predetermined feed path by using rotation of a feed roller.
An image forming apparatus, such as a copying machine and a printer device, in which an image is formed on paper, fed through a feed path from a paper supply unit to a paper discharge unit, by an operation of a print unit disposed on the feed path includes a paper feeding apparatus for feeding the paper by using rotation of a feed roller facing on the feed path.
The feed roller is connected with a motor shaft of a driving motor fixed within the body of the image forming apparatus through an appropriate rotation transfer device, so as to be driven by the motor. When a gear or a timing belt is used as the rotation transfer device, rotation irregularity can be unavoidably caused due to back crash.
In particular, when the rotation irregularity is caused in an image forming apparatus for forming a multicolored image in which print units corresponding to respective colors, i.e., black, yellow, magenta and cyan, are aligned along the feed path, a printing position can be shifted in the respective print units, resulting in disadvantageously degrading printing quality. Therefore, a rotation transfer device for directly coupling the roller shaft of the feed roller and the motor shaft of the driving motor through a coupling is used for preventing the rotation irregularity.
Also, in the paper feeding apparatus, in order to ease maintenance, inspection and exchange of the feed roller, which is unavoidably degraded with time, the feed roller or a feed unit including the feed roller can be taken out of the body of the image forming apparatus. Furthermore, in a practically used paper feeding apparatus, the feed roller or unit can be removed by drawing the transfer roller in the axial direction without affecting other composing members.
In order to make the feed unit removable by drawing the feed roller, it is necessary to couple the roller shaft (a driven shaft) of the feed roller with the motor shaft (a driving shaft) of the driving motor fixed within the body of the image forming apparatus removably in the axial direction. As a rotation transfer device with a simple structure enabling such removable coupling, one as is shown in FIG. 1 is conventionally used.
In FIG. 1, a reference numeral 1 denotes a roller shaft, that is, a driven shaft, of a feed roller, a reference numeral 2 denotes a motor shaft, that is, a driving shaft, of a driving motor. These shafts are respectively coaxially provided, at their ends, with coupling members 1a and 2a each in the shape of a short cylinder having substantially the same diameter. On the opposing faces of the coupling members 1a and 2a, transfer pins 1b and 2b are projected toward each other in positions away from the axial centers by substantially the same distance. The coupling member 2a is rotated in accordance with the rotation of the motor shaft 2, and the transfer pin 2b, which moves along a predetermined circle in accordance with the rotation, comes to a contact with the transfer pin 1b on the same circle as is shown in FIG. 1, so as to push the transfer pin 1b in the peripheral direction. Thus, the rotation of the motor shaft 2 is transferred to the coupling member 1a and the roller shaft 1.
Since these coupling members 1a and 2a are not at all constrained in the axial direction of the roller shaft 1, they can be easily removed from each other by moving the roller shaft 1 away from the motor shaft 2. Thus, the feed roller can be drawn. The feed roller can be any roller which can directly or indirectly feed paper, such as a sensitive drum used in an electrophotographic image forming apparatus and a driving roller of a transfer belt extended along the feed path.
Furthermore, when the feed roller having been drawn is pushed in again and the coupling members 1a and 2a are positioned to be close to and oppose each other by moving the roller shaft 1 toward the motor shaft 2, the rotation of the motor shaft 2 can be transferred to the roller shaft 1 again. At this point, the transfer pins 1b and 2b are not required to be positioned in the peripheral direction, but the rotation transfer can be attained merely by pushing the roller shaft 1 in.
The feed roller in an operation in the paper feeding apparatus, however, is supplied with rotation torque in the reverse direction to the driving direction of the driving motor by a function from the paper to be fed, and the rotation torque is varied. Therefore, when the rotation transfer device of FIG. 1 is used, the variation of the rotation torque can move the transfer pins 1b and 2b toward and away from each other, thereby causing the rotation irregularity. As a result, the aforementioned problem can occur.
On the other hand, Japanese Patent Application Laid-Open No. 8-87225 (1996) discloses a rotation transfer device which can removably couple a sensitive drum used in an electrophotographic image forming apparatus with a motor shaft of a driving motor. The rotation transfer device is disposed at an axial center portion of the sensitive drum, and includes a recess having internal teeth in the shape of a bevel gear, a male type member, having external teeth in the shape of a bevel gear along its periphery, which is fit around the motor shaft movably in the axial direction, and a compression spring for pushing the male type member in a direction toward its tip. The male type member is fit in the recess by a force applied by the compression spring, so as to transfer rotation through engagement between the external teeth of the male type member and the internal teeth of the recess.
Also in this rotation transfer device, the coupling can be released by drawing the sensitive drum in the axial direction as in the rotation transfer device of FIG. 1. Also, when the sensitive drum is pushed in and the motor is appropriately driven, the male type member moves forward by the function of the compression spring to be fit in the recess for attaining the coupling. Furthermore, since the coupling is attained by the engagement of the bevel gears, a shift and inclination in the axial centers between the sensitive drum and the motor can be absorbed, resulting in realizing definite coupling.
This rotation transfer device, however, requires precisely processed members such as the recess having the internal teeth and the male type member having the external teeth, and the structure is disadvantageously complicated. In addition, it is impossible to avoid rotation irregularity from being caused by back crash between the internal teeth and the external teeth. Therefore, when this rotation transfer device is used in the above-described multicolored image forming apparatus, it is difficult to retain good printing quality.